The present invention relates to determining biofuel concentration, and more specifically to determining biofuel concentration in petroleum-derived fuels.
Biofuels are being added more frequently to petroleum-derived fuels (also known as petrofuels), often times to supplement the more scarce or costly petrofuels. This type of fuel mixture is called a fuel blend, and may include a variety of fuels, such as biofuel, petrofuel, or any other fuel, or a combination thereof. One such fuel blend includes a low level of ethanol, a type of biofuel, and is referred to as E10. Another example of a fuel blend containing ethanol is called E15 and another example is called E85. And, yet another example of a fuel blend includes biodiesel, another type of biofuel.
Although biofuels have made their way into the market, some conventional engine systems are incompatible with fuel blends including biofuels. An incompatible system may be reconfigured for compatibility, but often times, this conversion process is expensive and labor intensive. Examples of biofuel incompatible systems still in use today include small engines used in lawnmowers, snowblowers, chainsaws, trimmers and other applications. Other example engine systems are included in small outdoor power equipment, recreational vehicles, off-road or farming equipment, and marine and aviation applications. Due to these compatibility issues, a consumer in possession of an engine system incompatible with biofuel may be motivated to obtain fuel that does not contain biofuels, such as ethanol. An ethanol free source may be difficult to locate, and there may be no guarantee that fuel advertised as 100% gasoline does in fact contain no ethanol by its outward appearance.
Some conventional engine systems may be compatible with biofuels, but because biofuels and petrofuels may exhibit different combustion properties, these conventional engine systems may adapt to operate as a function of biofuel content. In some cases, the system may be optimized based on biofuel content. One conventional engine system that has been configured to be biofuel compatible is the combustion engine powering many vehicles on the road, today. Other example engine systems that may be configured for biofuel compatibility include those mentioned above in connection with incompatible systems. These conventional engine systems may measure biofuel concentration in a fuel blend by utilizing a conventional sensor, also referred to as a flex fuel sensor. By measuring the biofuel concentration of the fuel blend, the system may adapt or calibrate itself for operation. But, these conventional flex fuel sensors are considered by many to be expensive, unreliable, and inefficient energy consumers. They may also be highly sensitive to contaminants, particularly to water, prevalent in many fuel blends.
For alcohol-gasoline fuel blends, such as ethanol-gasoline blends, two types of fuel composition sensors or conventional flex fuel sensors are often times used. The first type is an optical-based sensor that measures the refractive index, and the second type is a dielectric sensor that measures the dielectric constant of the field. Of these two types, the dielectric sensor is the most widely used. Both types, however, have two primary downsides: they are in many cases expensive to manufacture and maintain, and they may be highly sensitive to fuel contaminants, particularly water.
In contrast to petrofuels, such as gasoline or diesel, biofuels are often highly polar. The degree of fluid polarity may impact the electrical current produced in a dielectric sensor. For example, an increased polarity may cause an increase in the measured electrical current. Contaminants, particularly water, are also often highly polar, and may provide additional current contributions in the dielectric sensor that may not be distinguishable from the biofuel contribution. Thus, accurate measurements may not be obtainable using a dielectric sensor unless fuel contamination is low or below a threshold.
The refractive index (or optical) sensor may also be impacted by contaminants, such as water. This sensor technique may be less sensitive to contaminants than the dielectric method, but it is considered by many to be more complex in structure, and therefore more expensive. Additionally, optical sensors may utilize windows, such as a transparent or translucent material, through which to transmit a signal. These windows may become dirty such that maintenance and replacement are frequent considerations.